In a distributed database system data is located not only on one but on several different database servers. A lookup system is required in order to be able to route queries for a specific data item to a database server called back-end database server that stores this item. Pointers to these back-end database servers are stored in the lookup system which is also called front-end system. These pointers are generally of the format <key, value>, where the key is a valid search key for a back-end database server, and the value is an address of the back-end database server where the corresponding data item is located. Thus, when a query, e.g., an LDAP (Lightweight Directory Access Protocol) command, is issued to a distributed database system, it is first resolved in the front-end system (which is constituted by front-end servers, hereinafter also referred to as servers of a first server type), and then forwarded to the correct address in the back-end system (which is constituted by back-end servers, hereinafter also referred to as servers of a second server type), where it can be processed.
Recently, there is a trend in mobile network database system design to create only one logical database that physically runs on a multitude of servers and also unifies different types of databases, for example, HLR (Home Location Register), RADIUS (Remote Authentication Dial-In User Service), OAM DB (Operation And Maintenance DataBase), NM DB (Network Management DataBase), etc.
In conventional distributed database front-end systems the pointers as described above are saved in all nodes constituting the front-end system.